Audi A2 1.4TDI (75Hp) coolant temperature

A

albim1998

New Member
Hello everyone,
I own an Audi A2 production year 2001. I have seen many threads here about the coolant temperature sensor problem in many Audi A2. Mine though seems a little odd, as while city driving the temerature reaches 90°C (as it should) and I can see that it operates in the normal fuel range for urban driving (5-6 l/100km) but when in fast roads (inter urban) it goes to around 7 l/100km but I can also see the temperature gauge go below 90 to aroujd 70°C. (calculation is more of a guessing using the odometer and the portion of wated fuel) I know that the ECU when sees temps below 90 tries to add more fuel to the system to heat up the engine. Im not sure though if this water coolant temp is observed from the ECU or whether any other sensor is observed. Also I don't think the sensor is not working as in urban driving, the voolant temp does not move either above 90 or brlow 90. In all cases the heater has been off. Do you guys think is the thermostat staying open? Also another observation when the A/C is on on cold air while idling the temps tend to go down insted of up. I know I must have a vacumm leak somewhere as when in 5th gear at around 3000rpm the car goes in limp mode and turn off the turbo. Not sure if this is related but I still adeed it. Any help would be appriciated.
 
The first half of the post sounds very much like the thermostat. The Tdi is notorious for being difficult to warm up when you're not using much power to begin with, but will eventually get there in warm temperatures in urban conditions providing everything else is working. However, increase the airflow with a thermostat jammed open even in summertime and it will very quickly start draining the heat away. My car before thermostat replacement would read <60C at motorway speeds - and then when I hit a traffic jam, the needle suddenly went up to 90.

Temp sensor faults will manifest themselves as either no needle movement at all, or else something a bit like a light-switch : reading normally for a while, then suddenly vanishing after going over a pothole, then coming back again. Couple that with a dud thermostat (as was the case with my first A2) and your temp readings and fuelling will be all over the place. Typically you will get an error code along the lines of 'Coolant temperature sensor' 'open to earth - sporadic' or similar in the error codes in either the ECU or the dashboard fault code logs.
 
albim1998 said:
Hello everyone,
I own an Audi A2 production year 2001. I have seen many threads here about the coolant temperature sensor problem in many Audi A2. Mine though seems a little odd, as while city driving the temerature reaches 90°C (as it should) and I can see that it operates in the normal fuel range for urban driving (5-6 l/100km) but when in fast roads (inter urban) it goes to around 7 l/100km but I can also see the temperature gauge go below 90 to aroujd 70°C. (calculation is more of a guessing using the odometer and the portion of wated fuel) I know that the ECU when sees temps below 90 tries to add more fuel to the system to heat up the engine. Im not sure though if this water coolant temp is observed from the ECU or whether any other sensor is observed. Also I don't think the sensor is not working as in urban driving, the voolant temp does not move either above 90 or brlow 90. In all cases the heater has been off. Do you guys think is the thermostat staying open? Also another observation when the A/C is on on cold air while idling the temps tend to go down insted of up. I know I must have a vacumm leak somewhere as when in 5th gear at around 3000rpm the car goes in limp mode and turn off the turbo. Not sure if this is related but I still adeed it. Any help would be appriciated.
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Hi, when you get limp mode, it usually comes from overboost problem,first check those small rubber pipes which goes to N75 valve, they are cheap but some work to change, off course N75 can also been broken. VCDS scanning would make fault finding easier. Mine was those small pipes.
 
The first half of the post sounds very much like the thermostat. The Tdi is notorious for being difficult to warm up when you're not using much power to begin with, but will eventually get there in warm temperatures in urban conditions providing everything else is working.
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I'll reinforce Robin Cox, my TDi went in to a VW/Audi specialist for coolant temperature sensor replacement. This didn't solve the problem and replacing the thermostat has. It's now solid - once up to temperature - at 90c in both city driving and motorways.
 
Robin_Cox said:
The first half of the post sounds very much like the thermostat. The Tdi is notorious for being difficult to warm up when you're not using much power to begin with, but will eventually get there in warm temperatures in urban conditions providing everything else is working. However, increase the airflow with a thermostat jammed open even in summertime and it will very quickly start draining the heat away. My car before thermostat replacement would read <60C at motorway speeds - and then when I hit a traffic jam, the needle suddenly went up to 90.

Temp sensor faults will manifest themselves as either no needle movement at all, or else something a bit like a light-switch : reading normally for a while, then suddenly vanishing after going over a pothole, then coming back again. Couple that with a dud thermostat (as was the case with my first A2) and your temp readings and fuelling will be all over the place. Typically you will get an error code along the lines of 'Coolant temperature sensor' 'open to earth - sporadic' or similar in the error codes in either the ECU or the dashboard fault code logs.
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yeah I totally understand what you mean. I do not have vcds but I have a small cheap obd2 to wifi adapter which I can run and see any codes but nothing pops up there. Secondly in city driving, as I said, the temp stays 90 firm and only on highway it drops below even if hard driven which logically should directly relate to the thermostat being stuck open and overcooling the engine. I eill chsnge the thermostat today and see if any changes occur.
 
sonicci said:
Hi, when you get limp mode, it usually comes from overboost problem,first check those small rubber pipes which goes to N75 valve, they are cheap but some work to change, off course N75 can also been broken. VCDS scanning would make fault finding easier. Mine was those small pipes.
Click to expand...
I was checking the N75 valve which I beleive is located up the engine bay under the glass window. It is indeed kinda hard to change that tube. I can see teo issues. First one is that one of the tubes coming out of the N75 valve and the EGR have fresh oil onto them. Secondly, one of the tubes coming out of the N239 and that goes into some kind of leg which is connected to the EGR valve( guessing that is what triggers it to be open or closed) is kinda worn out. From what I can see from the Audi Workshop Manuals that must be the varibale intake manifold which to br honest I do not completely understand what it does. I will also consult with the mechanic today to see if we can solve anything.
 
The vacuum tubes going to the EGR on an AMF is the anti-shudder valve actuator, and the EGR mixing valve thing ; there is one that goes to the turbocharger that actuates the wastegate. If there is oil coming through your EGR it could be worn turbo bearings - that is what has my project car out of action at the moment pending a turbo replacement - it was very oily down the back of the engine since I've had the car, but what with diesel pump leakage and other restoration jobs last year that wasn't the first thing that needed doing as the car itself was running really well.

Not sure what the variable intake manifold is on a 75hp diesel - are you sure you've not confused it with pages for the 1.6Fsi?
 
Robin_Cox said:
The vacuum tubes going to the EGR on an AMF is the anti-shudder valve actuator, and the EGR mixing valve thing ; there is one that goes to the turbocharger that actuates the wastegate. If there is oil coming through your EGR it could be worn turbo bearings - that is what has my project car out of action at the moment pending a turbo replacement - it was very oily down the back of the engine since I've had the car, but what with diesel pump leakage and other restoration jobs last year that wasn't the first thing that needed doing as the car itself was running really well.

Not sure what the variable intake manifold is on a 75hp diesel - are you sure you've not confused it with pages for the 1.6Fsi?
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I see I see. So I should also check the turbo thank you for the info. I was rechecking the manuals and no I am not mistaken but it seems some kind of solenoid which has one tube going into the egr and the other going into the main intake into a sensor which I think it i
Robin_Cox said:
The vacuum tubes going to the EGR on an AMF is the anti-shudder valve actuator, and the EGR mixing valve thing ; there is one that goes to the turbocharger that actuates the wastegate. If there is oil coming through your EGR it could be worn turbo bearings - that is what has my project car out of action at the moment pending a turbo replacement - it was very oily down the back of the engine since I've had the car, but what with diesel pump leakage and other restoration jobs last year that wasn't the first thing that needed doing as the car itself was running really well.

Not sure what the variable intake manifold is on a 75hp diesel - are you sure you've not confused it with pages for the 1.6Fsi?
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If u see number two on the list that is what I am talking about.
 

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audifan said:
Anti shudder valve.
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Okay, that explains the rough shutdown of the engine. As per info I tried changing the sensor and no result but as expected the sensor was not the problem but rather the thermostst which i will change today. I saw that the bottom bolt was a bit had to open without a small cricket and hopefully I can find one.
 
Update: Okay I am going to start with the fact that that lower bolt was a pain in the a$$. I tried bolting it out in using the ball end allen key to using a small click/torque wrench and both of them gave no results when the alternator was in place. Actually the ball end allen key damaged the socket as I put a little too much force onto it so beware other people who want to do this repair on their own. At that point I just removed the alternator (a pain of itself to be removed as the engine bay space in the A2 is awfully small) and the thermostat screw came out in no time. I noticed that the thermostat that I removed was OEM (almost 19 years, when I had a W201 I remember I changed the thermostat twice for the 10 years I had it) and indeed it was a tiiiiiny bit open. After changing it with an aftermarket part (here in Albania OEM stuff is non existent and if they tell you its OEM, it is 99% of the times a lie) the engine heats up normally and the fuel efficiency is right where it should be. Thank you very much for your advice. As for the Limp mode at high load, I did check the N75 valve and it seems to work correctly when tested on a bench but not sure if it is misbehaving when driving. I could not find any air leaks before or after the turbo ( I did not check the intercooler though) but a guy here told me that these cars have a way to go into limp when driven hard as to prevent drunk people from driving to fast or something like that. I remember reading some stuff like that somewhere on the Internet some years ago but I generally do not believe this is true.
 
I replaced my thermostat today on my 1.4TDi and using the correct offset 10mm spanner it was a breeze. I was advised that this is the way to do it on a FB A2 forum. I purchased a set from Machinemart for £16 as a 10mm on it's own from Halfrauds was £is so it seemed a logical step.
 
I was going to start a second post about what I considered to be rather low temperature on my '03 TDi. It only gets up to about 73/74 deg in town and about 69-70 the rest of the time. I take it this means the thermostat is failing, or has failed. It has been mentioned that this adversely affects fuel consumption. Is this correct?
 
Veedub68 said:
I was going to start a second post about what I considered to be rather low temperature on my '03 TDi. It only gets up to about 73/74 deg in town and about 69-70 the rest of the time. I take it this means the thermostat is failing, or has failed. It has been mentioned that this adversely affects fuel consumption. Is this correct?
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Yes, that is correct. I used to get high fuel consumption especially during high way travel as in the city it used fairly normally. Many people were able to get to bottom screw of the thermostat without removing the alternator using a ball-end Allen key or a small wrench but for me the Allen key did not work (it actually wore out the inside of the screw) and I had to remove the alternator (adds about half an hour to 45 minutes to the removal as the alternator belt is hard to remount(it might just be me not having the right tools for the job. The alternator had a screw on the top and two on the bottom of it on the side of the best (I might be wrong as it has been some weeks). Try not to buy a cheap thermostat though as they tend to break easily so ask around for the best longevity to price thermostat. If the problem persists then it must be the coolant temperature sensor which is located at the right, middle, back of the engine. What I am seeing different from your case is that my temps would rise up to 90 while hard city driving (low gears, high rpms) but on high ways it was something like what you have. Also to take the temperature to 90 it used to take a long time. It definitely helped with the fuel efficiency of the car. A2 workshop manuals (A2 Workshop) can help you a lot, if you want to do it on your own. Just to rule out your sensor is not faulty you can try to see if it reaches 90 while doing what I did just for a drive (this are just the way I do so, this is not advised anywhere but the way the water cooling system works and the temp sensor works, this way should give you a definite answer toward a thermostat stuck open almost completely or a faulty sensor). The definite way I think is to change the thermostat before the sensor as the sensor is hard to get (at least where I live). If the problem of consuming to much fuel would persists, I would suggest to check the fuel lines first, injectors second, maybe the turbo and if none of these it can be a piston compression fault if u also have loss of power and oil (very very not likely as these engines are actually really sturdy).
 
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albim1998 said:
Yes, that is correct. I used to get high fuel consumption especially during high way travel as in the city it used to heat up a lot. Many people were able to get to bottom screw of the thermostat without removing the alternator using a ball-end Allen key or a small wrench but for me the Allen key did not work (it actually wore out the inside of the screw) and I had to remove the alternator (adds about half an hour to 45 minutes to the removal as the alternator belt is hard to remount(it might just be me not having the right tools for the job. The alternator had a screw on the top and two on the bottom of it on the side of the best (I might be wrong as it has been some weeks). Try not to buy a cheap thermostat though as they tend to break easily so ask around for the best longevity to price thermostat. If the problem persists then it must be the coolant temperature sensor which is located at the right, middle, back of the engine. What I am seeing different from your case is that my temps would rise up to 90 while hard city driving (low gears, high rpms) but on high ways it was something like what you have. Also to take the temperature to 90 it used to take a long time. It definitely helped with the fuel efficiency of the car. A2 workshop manuals (A2 Workshop) can help you a lot, if you want to do it on your own. Just to rule out your sensor is not faulty you can try to see if it reaches 90 while doing what I did just for a drive (this are just the way I do so, this is not advised anywhere but the way the water cooling system works and the temp sensor works, this way should give you a definite answer toward a thermostat stuck open almost completely or a faulty sensor). The definite way I think is to change the thermostat before the sensor as the sensor is hard to get (at least where I live). If the problem of consuming to much fuel would persists, I would suggest to check the fuel lines first, injectors second, maybe the turbo and if none of these it can be a piston compression fault if u also have loss of power and oil (very very not likely as these engines are actually really sturdy).
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Thank you for your very comprehensive response. I'm going to have a look at the thermostat (if it ever stops raining) and determine whether I'm going to have a go at it myself. With you mentioning cheap thermostats, I might go to a motor factor and buy one, as this will hopefully ensure a part of decent quality.
 
Veedub68 said:
Thank you for your very comprehensive response. I'm going to have a look at the thermostat (if it ever stops raining) and determine whether I'm going to have a go at it myself. With you mentioning cheap thermostats, I might go to a motor factor and buy one, as this will hopefully ensure a part of decent quality.
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Depending on where you live you can try AUDI genuine parts. It lasted on my car for 19 years which I think is really impressive. I cannot really find original parts here in Albania but what I bought seemed good and it was at around 17 Euros so somewhere around that price should be okay. Just make sure to bleed out the air correctly. If you need help with that I can help you out.
 
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